In recent years, the popularity and growth of cellular communication has increased in dramatic fashion. In fact, current cellular networks are being continually pressed to keep up with the demands for increased capacity and more reliable service. One of the fastest growing parts of the cellular communication market is the transmission of data over cellular networks. The users of cellular services are more and more combining the functionality of portable data terminal equipment (DTE), e.g., a lap-top personal computer or personal digital assistant, with cellular data communication equipment (DCE), e.g., a modem coupled to a cellular phone, in order to serve both professional and personal needs. It has recently been suggested that approximately 3% of the cellular calls made in North America are data calls, and all indications are that this number will only increase in the future. Accordingly, the growth of this data communication market is placing additional demands on the current cellular networks to provide faster and faster data rates. While present day modems are able to transmit data at rates up to 33,600 bits per second (bps) over land-line communication channels, such speeds are not yet achievable in cellular communication because of Rayleigh fading, co-channel interference, etc., which essentially increase the error rate by increasing the noise on the cellular channel. Those in the art have realized that one way to improve data transmission rates in the cellular environment is to use a data protocol that is better suited to combating the effects of the cellular environment over the cellular portion of the data connection. One example of a cellular oriented protocol is the Enhance Throughput Cellular.TM. (ETC.RTM.) protocol developed by Paradyne Corporation, Largo, Fla., U.S.A.
Nonetheless, even with a cellular-oriented protocol, other impairments limit the effective data rate over a cellular channel. One such impairment is the encoding scheme utilized over the communication link interconnecting a cell site transceiver and the mobile telecommunications switching office (MTSO). This link (also referred to as a carrier facility) is most typically a T1 trunk in the North American cellular system, and an E1 trunk in the European cellular system. In order to increase the bandwidth of the carrier facility, cellular service providers make use of voice compression encoding schemes such as adaptive differential pulse code modulation (ADPCM). For example, a T1 trunk with 24 DSO slots can accommodate up to 48 ADPCM channels, where alternatively, the same T1 trunk can only accommodate 24 channels when utilizing pulse code modulation (PCM). Thus, the use of voice compression increases the capacity of the cellular network, and thereby reduces the number of T1 trunks necessary to connect each cell site transceiver to the MTSO. As appreciated by those knowledgeable in the art, this is an important concern of cellular service providers since each carrier facility, that is, each T1 trunk, has associated with it a substantial cost.
While compression schemes such as ADPCM have no discernible effect on voice transmissions, they do limit the maximum data rate for data transmission to approximately 9,600 bps. This is primary because voice compression schemes introduce noise into the data signal that cause the data modem at the MTSO to reduce its effective data rate via autorating, as is well known in the art. Moreover, the greater the compression of the signal, the greater the amount of noise introduced, and consequently, the lower the data rate. Therefore, cellular modems connected to a channel utilizing an encoding scheme with little to no compression such as PCM can presently achieve data rates up to 21,600 bps, a significant improvement over channels utilizing a voice compression encoding scheme such as ADPCM which limit the modem's data rate to approximately 9,600 bps. The problem still exist on how to harness this improved performance in data rates with uncompressed channels without dramatically reducing the capacity of the carrier facilities.
Presently, most cellular networks provide a mixture of compressed (i.e., ADPCM) and uncompressed (i.e., PCM) channels in the carrier facilities that are interconnecting the cell site transceiver and the MTSO. When a new user in a particular cell requires one of the channels as a carrier facility for communication, the MTSO typically uses a hunt group to locate and assign an open channel to that user. This is usually done in one of two methods. A first method is to assign the new user to the first open channel in the hunt group, that being the available channel with the lowest channel number. This is referred to as fixed order hunting. A second method is to assign the new user to the next sequential channel in a hunt group. This is referred to as rotary hunting. As is evident, neither of these methods provide any optimization of the uncompressed channels for data calls or the compressed channels for voice calls. All things considered, the probability that a data call would be routed to an uncompressed channel of the carrier facility using either method is uncontrollable, if not unpredictable.
Thus, a need exist in the industry for a system and method for maximizing the utilization of uncompressed channels for data calls and compressed channels for voice calls in order to increase the effective data rate in the cellular portion of the data connection and to improve the overall performance of the cellular network.